From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1C04A3101B2 for ; Wed, 19 Aug 2026 12:50:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787143835; cv=none; b=ZTVN40XTk1NjaQ143BSISaGcOnVg64+Q+Bh/xokEQRSuoxftjvnGROj9ZbRYCZz2B9cAcRzI5x8v9ni8ieX/9LMLC7DM8ulmsWrfkrsxJvaY+R7FCsk/YBbaE2HjG9JqCqyqAzw+OLlEWq2shm6LO5bFUzzr2bShvjuti54NcIw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787143835; c=relaxed/simple; bh=vfppvCG/qvbrNitjequc3qq46dLMqTHjUV4R5KJVO7E=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=MmC7XSHI1Ry28w77BALcw27qbcyI2YO5FmoCdamUf6K8mH5eKRrOS0tyme1tf75k71kcvlKozDR08Mac7UQ969C3TPptf5+37jgcgkf2dauCx7ZBkXf7LXYZlN+4CZXWrK/lLH4WOaC2PUkBRvfK7JxAdpotI0oQ8PlNFzjsp6U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=WVoVn3pQ; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="WVoVn3pQ" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1787143831; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+KudDx4GWA6m0kymTqV9B5+pPC4d5wMXWeaLZi91N90=; b=WVoVn3pQZT4ckT9uj8kHO+a00+NS4ANKdXhr0BPgcRXqep8ettJ/A8MFIlvTwXq0ozBzrq su0J9bz1fRLy4IU+ooJfSlPCcudteInHCU2bJN8oP9pTOK8bXR5a98f4GW9au9HrwTTdFJ +wm/yvRcMTD5pzBDmnNuy/c51qo4n6o= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-331-INSEtobNO6C9huKBqR73aQ-1; Wed, 19 Aug 2026 08:50:25 -0400 X-MC-Unique: INSEtobNO6C9huKBqR73aQ-1 X-Mimecast-MFC-AGG-ID: INSEtobNO6C9huKBqR73aQ_1787143824 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id D55061955DBE; Wed, 19 Aug 2026 12:50:22 +0000 (UTC) Received: from fedora (unknown [10.44.33.127]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id A33BE180034F; Wed, 19 Aug 2026 12:50:17 +0000 (UTC) Received: by fedora (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 19 Aug 2026 14:50:22 +0200 (CEST) Date: Wed, 19 Aug 2026 14:50:16 +0200 From: Oleg Nesterov To: Christian Brauner Cc: Jens Axboe , Peter Zijlstra , Alexander Viro , Jan Kara , Steve French , linux-fsdevel@vger.kernel.org, bpf@vger.kernel.org, linux-cifs@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 0/4] Stop TIF_NOTIFY_SIGNAL from interrupting work that can't be restarted Message-ID: References: <20260818-work-tif_notify_signal-v1-0-1ee1fcc5b3ff@kernel.org> Precedence: bulk X-Mailing-List: linux-cifs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260818-work-tif_notify_signal-v1-0-1ee1fcc5b3ff@kernel.org> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Hi Christian, I am still travelling without my work laptop, can't read the code. I'll try to take a look on Friday. IIRC, zap_pid_ns() can use the new helper too... Oleg. On 08/18, Christian Brauner wrote: > > Ok, so I was looking into things and as usual got > side-tracked so here we are. Oleg, save me please. > > IF_NOTIFY_SIGNAL is used to kick a task in uninterruptible sleep to > return to userspace and run task work and then go back to sleep. This > mechanism works well but breaks coredumps. dump_interrupted() only > allows fatal signals to interrupt a coredump and the whole regular write > path going to actual filesystems is impervious to TIF_NOTIFY_SIGNAL as > well. > > The core is that you can have quite deep callchains that end up calling > signal_pending() in both the pipe and the socket codepaths so it's like > we can just pass a flag through somehow. > > For coredumps its very annoying because it means io_uring is - depending > on how much outstanding work you have - incompatible with generating > non-truncated coredumps. A process with too many file backed mappings > and io_uring requests in flight ends up losing most of the coredump. > > While zap_threads() has cleared TIF_SIGPENDING for a long time, just > clearing TIF_NOTIFY_SIGNAL isn't going to work because the next > completion will just set it again. > > The fun part also is that io_uring isn't actually the only case: > > (1) io_uring > > (2) klp_send_signals() > > (3) bpf_task_work_schedule_signal() > > (4) landlock's tsync > > And technically, kthread_stop() and the printk kunit test set the bit > raw. So no simple way of just fixing this in one subsystem. > > So, a fix for this issue has the following constraints: > > (i) The places where a write is aborted are deep callchains that we > can't reasonably parameterize. For example, anon_pipe_write(), > unix_stream_sendmsg(), unix_stream_read_generic(), > sk_stream_wait_memory(), or a bare wait_event_interruptible() in > wait_for_dump_helpers(). All of them are shared with regular > syscalls that must stay interruptible. > > IOW, the state has to be per-task and ambient. > > An LLM would call this "load bearing"... > > (ii) There are multiple ways TIF_NOTIFY_SIGNAL can get raised and they > can get set from irq context against any task. As said above we > have at least io_uring paths (poll task_work, msg_ring, tctx exit, > io-wq via __set_notify_signal()), bpf_task_work_schedule_signal(), > klp_send_signals(), landlock tsync, plus kthread_stop() and the > printk kunit stuff that set the bit raw. > > So fixing this up in the individual subsystems is doomed to fail or > require constant audits in case some new variant shows up. > > (iii) The coredump task is exiting and can't restart the work. > > So here's some stuff that was considered but I think it not really > feasible: > > (a) Check for task_is_coredumping(). That will end up forcing > task_work_add() users to know about coredumps. This seems like a > layering violation. > > I have a patch for this as well but it's ugly. It races with the > dump staarting unless the bit setter takes a lock in the io_uring > completion. I know someone that will disagree with this approach. ;) > > (b) Oleg's old suggestion iirc. Just clear the bit at coredump entry. > That doesn't work because io_uring poll completions just raise it > again from irq context. So you also need synchronization with the > setter of which there are quite a few. > > (c) Let the setting task defer setting the bit if the task is flagged > and then raise it again at exit. > > (d) Take TIF_NOTIFY_SIGNAL out of singal_pending() and make it opt-in at > specific points. That breaks io_uring quite badly and forces a > tree-wide audit. > > So the amount of patches for this issue over the years is impressive. So > let me add one to the pile for the lolz. > > Add PF_NO_NOTIFY_SIGNAL and helpers to raise/restore it. This is the > same approach as memalloc_nofs_save(). signal_pending() will not report > a fake pending signal via TIF_NOTIFY_SIGNAL if inside a > PF_NO_NOTIFY_SIGNAL critical section. Obviously you can't > fork()/clone3() in such a section. > > Fix coredumps and smb. Fwiw, I think there's a few other potential users > of the helpers that are left out of this series. > > | | notify_signal_pipe | notify_signal_socket | > |---------|---------------------------|---------------------------| > | fix | ok | ok | > |---------|---------------------------|---------------------------| > | unfixed | 357324 of ≥ 5111808 bytes | 467336 of ≥ 5111808 bytes | > > Signed-off-by: Christian Brauner (Amutable) > --- > Christian Brauner (4): > signal: allow taks to temporarily block TIF_NOTIFY_SIGNAL > coredump: prevent TIF_NOTIFY_SIGNAL from interrupting coredumps > selftests/coredump: test that TIF_NOTIFY_SIGNAL doesn't truncate a coredump > smb: prevent TIF_NOTIFY_SIGNAL from interrupting > > fs/coredump.c | 4 + > fs/smb/client/transport.c | 13 +- > include/linux/sched.h | 2 +- > include/linux/sched/signal.h | 21 +- > tools/testing/selftests/coredump/Makefile | 7 +- > .../selftests/coredump/coredump_notify_signal.h | 29 ++ > .../coredump/coredump_notify_signal_helper.c | 46 +++ > .../coredump/coredump_notify_signal_test.c | 245 ++++++++++++++++ > tools/testing/selftests/coredump/coredump_test.h | 1 + > .../selftests/coredump/coredump_test_helpers.c | 318 +++++++++++++++++++++ > 10 files changed, 674 insertions(+), 12 deletions(-) > --- > base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f > change-id: 20260817-work-tif_notify_signal-6ab080d33693 >